Russian Roulette, Unfaithful, Take a Bow, Drunk On Love, Fool In Love are all great ballads and some of her best songs ever.
EDIT: Sorry, I read the title as "will Rihanna ever have a great ballad?". Well, my point still stands anyway. Fool in Love and Drunk On Love are some of her best songs. We All Want Love is great too but I wouldn't consider that a ballad. And Farewell *****.